Military Services Act 1916

The Military Services Act 1916 was passed in order to form a Reserve Expeditionary
Force where every European male between the ages of 20 and 46 was obliged to register eligible for military service and as a result could at a point in time be called up to serve by Ballot.

The Act was implemented as the need for more men at the Front was required than of those volunteering. 

Between 1916 and 1918 however men continue to volunteer in their thousands with 26,000 volunteering and 32,000 conscripted by ballot.

Initially Maori were exempt from the Act but were included in 1918.

From the outbreak of war in 1914 to the armistice in 1918, 124,211 New Zealand men served with the Expeditionary Force out of an eligible male population of under 250,000.
(Figures taken from the Te Ara Encyclopedia website http://www.teara.govt.nz/en/1966/compulsory-military-training/3)

No one would deny that New Zealand certainly contributed its fair share to the War effort in terms of men.